Adjusting Historical Stock Prices for Splits and Other Corporate Actions

Summary

The document asks how to convert a recorded purchase price into a value comparable with a stock’s current split-adjusted historical series. The example concerns an older Apple purchase, and the writer notes that splits and other corporate actions can change share counts and quoted prices. They consider estimating a conversion with regression but lack the corresponding unadjusted historical prices.

The text contains only the question; it provides no answer, adjustment method, evidence, or data source. It therefore highlights a practical historical-data problem without teaching how to solve it. Any usable conversion would depend on what adjustment is intended and which corporate actions the data provider includes. In particular, a split-adjusted price series and a series adjusted for distributions can represent different conventions, so the desired comparison must be defined before choosing data. The proposed regression is not evaluated in the document.

Key ideas

• Historical share prices may need adjustments to compare values across corporate actions.
• The question distinguishes split effects from other changes that affect share counts or prices.
• The author proposes regression as a possible conversion but supplies no supporting method or results.
• The document does not identify a data source or explain which adjustment convention to use.

Tags

# how to adjust very old stock price correctly


# how to adjust very old stock price correctly












lets say that i have a file stating a stock and the price which someone paid for it and the date. for example: apple (AAPL) 422$ 15/11/2011.

now apple have gone through many splits and possibly public offerings, or maybe increased their treasury stock numbers and any other activity which might affect the the number of stock available and the price of each stock. the problem that i have that historical data is adjusted for splits and all of the changes. and i wish to know the price that someone would pay with all the adjusting (something like 15$ in the apple example).

how can i convert that 422 dollars to the 15 dollars? i have many stocks, each one with different date and price. looking for a safe way to do those, and deviding by stock splits doesn't feel safe to me since stock splitting isn't the only option the change the price.

one idea i had is to use linear regression with x as the closing prices in the past (like 400) and y with the public adjusted data that i have (like 14.8) and use the result to convert 422 to 15. but i also can't find historical data with the 400 prices for 2011, all i find is adjusted. any idea how to convert?

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.